Telephone-exchange system.



PATENTED APR. 24

E. LAND. I TELEPHONE EXCHANGE SYSTEM.

APPLICATION FILED MAR. 20, 1905.

I 4 sHE TssHEET 1.

niunaizcznal wiinesss 1520622 for, MAM/2e fii AYEOYQRQQ/W.

PATEN-TED APR. 24, 1906.

I E. LAND. TELEPHONE EXCHANGE SYSTEM.

APPLICATION FILED MARJQ, 1905 4 SHEETS-SHEET 24 Edmuna Zand,

j, m% A zibrng t No. 818,540. PATENTED APR. 24, 1906.

E. LAND. TELEPHONE EXCHANGE gYSTEM.

APPLICATION FILED MAR-.20, 1905."

4 SHEETS-SHEET 3.

. v Z'YdmuncZLand', YU z'Znesses: fizz/swim JwWZ@M/M 6 I PATENTED APR. 24:, 1906.

E. LAND.

TELEPHONE EXCHANGE SYSTEM.

APPLICATION FlLED MAR.20,1905.

' 4 SHEETSSHEET 4.

Edmunoziamz iin esses:

UNI-TED srAT s PATEN- on EDMUND LAND, on GRAND RAPIDS, MICHIGAN.

No. s aseo.

To all whom it may concern; I

Be it known that I, ,EDMUNDLAND, a-citizen of the Dominion of Canada, and a resi dent of Grand Rapids, county of Kent, and Stateof Michigan, have invented a new and useful Improvement in Telephone-Exchange Systems, of Which the following is a specifie cation.

My invention pertains to semiautomatic telep'honeeexchange cquipment. By the term semi-automatic Iindicate those systems in which automatic selecting equipment is supplemented by the attention of a central-office operator who assists in promoting the connection tothe desired station.

I provide a system of keys for automatic selecting, ringing, and supervising with asso ciated -C1I'Oll1llS and automatic selectlng switches which will give to. the central-office of manual supervision of the connection.

In the drawings, Figure 1 is a general circuit diagram of my invention, the figure being drawn on two sheets designed to be placed end to end to'compl'ete the figure.

the off-normal switch of Fig. 3.

diagrammaticdetail of the automatic switch Fig. 2 is a diagrammatic detail of the switch forming a part of the line equipment 16. Fig. 3 is a diagrammatic detail of the automatic switch 23. -Fig. 4 is an additional detail of Fig. 5 is a 88, and Fig. 6 shows diagrammatically an alternative form of selecting-key device for the opera tors equipment 41.

Relays, keys, visual signals, 850., are shown in conventional form, as my invention does not in anyway involve ,the mechanical detail of the respective parts of apparatus used.

At 10 is shown a common battery substationltelephone equipment of a well-known type in which circuit through conductor 1 1 is closed for-direct current when the hook is up, and circuit through a condenser 12 and hi hresistance. ringer 13 is closed for alternating I Specification of Letters Patent. Application filed March 20, 1905. Seicial No. 250.933.

No flexible cords are used Patented April 24, 1906.

current when the hook is down. This substation telephone is connected by line conductorsl i and 15 with an automatic central office equipment pertaining individually to that line and indicated as a whole at 16..

The line equipment 16 consists of an automatic circuit-selecting switch of any desired mechanical type, the associated operatingmagnets of said switch, relay-armatures, and contacts for said operating-magnets, and an associated relay 17, not necessarily mechan-.

ically a part of said automatic switch. 111

ELEPHd EeEXcHANGE SYSTEM. 1

said automatic switch 18 is a magnet adapted to propel the moving part of the switch,

and 19 is a magnet adapted to release said moving 1part for restoration to its normal position o' gravity. 20-21 22 are -moving contact terminals or Wipers attached to the moving part of said automatic switch and adapted. to make contact with fixed terminals or Waiting contacts as'those shown associated withcon d-uctors 25 2624.

In mechanical design the automatic switch -mechanism-of the equipment 16 may be of any desired form, a diagrammatic represen-- tation of the conditions required for this switch being shown in Fig. 2, in which the designating numerals given are those of Fig.

rest through action of springs or 1, some further" parts being designated by letters.

In Fig. 2 B is a shaft supporting insulated wipers 20 21 22.. A is a ratchet mounted upon the shaft B. C is'an armature for mag net 18.

D is a pawl pivoted upon armature C. K is a fixed pin guiding pawl 13.. H is a pin upon pawl. G is a pin upon pawl M. E is an armature for magnet 1 9.- F is a link pivoted upon arma-tureE and having a hook projection to engage pin G, and a straight arm projection to be engagedby pin H. In operationsuccessive energizations of magnet 18 i will attract armature C successively, and thus cause driving-pawl D to propel ratchet A one tooth for each such energization, the ratchet A being held in its determined position by the detent-pawl M. Following this the energization of magnet 19 will attract its.

pawl D'., M is a pivoteddetent,

armature E, causing link F to pass forward until its hook projection passes over pin G,

the ratchetA being retained by detent-pawl M during the continuance of the energization of magnet 19. Upon denergization of magnet 19 and consequent release of armature E and return of that armature byspring tension to its position of rest link F. retirest'oits normal position of rest, and in doing'so its hook 'proje ction engages pin G on (letent+ pawl'M and withdraws said detentpaw1 from engagement with ratchet A.. Ratchet A therefore is released and now may return to its normal .position of rest .by action of springs or gravity.

Upon the next energization of magnet 18 and consequent movement of armature C and pawl 1) pin H engages link Fa-nd lifts it until it's hook projection is lifted out of engagement with pin G, thus releasing detent*l- .:pawl M to act as, previously mentioned. v v

, Referring again to Fig. 1, the step-by-step movement of the wipers 20 2122 causes them tion' is made with the waiting contacts of'a' v to make contact successively with the waiting contacts shown adjacent thereto until connectrunk not already in use, when connecting-1e lay 19 is energized, resulting'in the stopping of the motion ofthewipers and in the connecting of the line conductors 14 15 to the'wipers'21 {with keys and signals, as shown in the lower portion of Sheet L, and with an automatic selecting-sw1tch,(designated as a whole 23 in Sheet R,)the trunk thus terminating in armature parts of relay 56 and being connected through armature-contacts to magnets 54 and55 when the switch 23 is not in use. The trunk-conductors are 'two innumber, (indicated as 24- 25,) and they are multiplied through the'waiting-contacts of a plurality of automatic switches pertaining to line equipments, as 16, and an auxiliary conductor 26 .also' 18 multiplied through the waiting contacts of those automatic switches for purpose of busy test. Each trunk thus is l 11 14 29 22 24 39 and to ground without such 4 interruption in changing as would affect re-' lay 17 The energization of relays 17 and 19 accessible from ,a plurality of automatic switches,and' each automatic switch has accessible a plurality of trunks.

The action of the line e uipment 16 in selecting a trunk not alreaiiy in use is as follows: Upon removal of the receiver from the. hook at substation-telephone current flows from battery 27 through conductors 28 1 1 14,29 and to ground, energizing relay 17 and attracting its armature. The energization 5 of relay 17 gives path for current from battery through conductors 30 3132 33 20 34 and to ground, energizing actuating-relay 18,

which propels wiper 20 into connection with waiting-test contacts of the trunk 24 25, and wipers 2122 into, connection with conductors 2425. The attraction of the armature of relay 18 has interruped the circuit last de-v scribed-by breaking the connection between conductors 30 and 31; but this interruption has. de' ene'rgized relay 18, and upon the release of its armature the previously-described circuit is completed again as far as wiper 20. If at this time trunk 24 25 be alreadyin use, a

ground will be foundupon test-conductor 26, and circuitwill be completed for battery 27 over conductors 30 '31 32 33 20 26 and to ground, energizing relay 18 and stepping wipers 202 1 22 forward to the next trunk. This cycle of operation will repeat automatically,so long as wiper 20 finds a ground upon the testconductor of the trunk connected with, but as soon as a trunk is found whose test-conductor, .as 26," is. not grounded. the circuit from the wiper 20 to ground will not exist,

' and current willflo w from battery 27 over conductors 30 31 36, 35 and-to ground The resistance of relay 18 is low, and the number ofturns of the conductor30 upon relay 18 is comparatively small, while the relay 19 is of high resistance, and the number of turns of conductor 36 upon relay l9 is comparatively large. Furthermore, the spring tensions u on the armatures of-those relays are capabl e of relative adjustment. In response to this current through relays 18 and 19 in series the relay'18 is not sufficiently energized to attract its armatures or to break its armature-contact, while the relay 19 is energized to operate its armatures. Conductor 33 is removed from conductor 32 and placed in connection with conductor 37, thus placing a ground upon wiper 20 and upon test-conductor 26, and thus upon the multiplied testcontacts of the trunk 24 25, preventing the connection with that'trunk of any telephoneline through its equipment, such-as 16, and x I reserving that trunk exclusively for the use i of telephone-line 14 15 and the substationtelephone 10, The armatures of the relay 19 also have connected conductors 29 and 38 to wipers '21 22, and therefore-to conductors 24 25. Current previously flowing from bat tery 27 to conductors 28. 15 11 14 29 and to ground now flows through conductors 28 15 therefore is continued and calling visual sig nal 40 is displayed before the operator-using served by the signal 40. The circuit conditions now existing and which will remain uiichanged throughout the further promotion and continuance of the connection ive a cur rentfrom the battery 27 through t e speechtransmission device of the substation 10 in series with the conductors forming windin of relay 17, between one side of the line an current for speech transmission from the substation 10 without unduly detracting from, speech transmission to substation 10. Conequipment 41, indicating to her that a call ing patronhas been connected to the trunk ductors 42 43 44. provide for calls in which substationlO is the called station to the connals 40 and 45 and keys 46 47 48 49 50.51 52 53, located in a switchboard accessible visually and manually to the operator using the equipment 41, also automatic switch 23, located in the same central oflice with the operator 41. The switch 23 is'of a type having two directions of motion in its wipers, the first direction being controlled by actuating magnet 54 and the second motion being controlled by actuating-magnet 55. By the first motion, as in the vertical steps of a Strowger switch, wipers move to a'desired position, constituting by the selection of the position the selection of-a group of trunks i. 6., a group of sets of waiting contacts. By the second motion, controlled by magnet 55, the wipers are moved, as in the rotary motion of a Strowger switch, to select one set of contacts from the group of sets preliminarily-selected. Magnet 56 is a connecting and releasing magnet, and magnets 55 56-bear the same relation between themselves as do mag- 73 is an oil-normal switch.

ondary direction of selection.

nets 18 19, described in connection with switch 16 as will be seen in the detailed description of the operation of switch 23 immediately following. v

The automatic switch 23 may be of any preferred mechanical detail, one possible association of necessary parts being shown diagrammatically in Fig. 3.

In Fig. 3, 200 is a movable shaft sustaining the wipers 80 8182. 201 is a cylindrical rack upon the shaft by which the wipers may be moved in the primary direction of selection. 202 is a cylindrical ratchet upon the shaft by which the wipers may bemoved in the sec-.

203 is a detent-pawl adapted to engage both the cylindrical rack and the cylindrical ratchet to hold the wipers in the determined position both in primary and secondary directions and to release the wipers from restraint in both directions of selection when it is withdrawn. 205 is a pin upon pawl 203. 204 is the pivot upon which pawl 203 moves and by which it is sustained. 206 is an armature for magnet 54. 207 is a driving-pawl pivoted upon armature 206. 208 is a fixed pin acting as guide for driving-pawl 207. 209 is an armature for magnet 55. 210 is a driving-pawl pivoted upon armature 209. 211 is a fixed pin acting as guide for driving-pawl 210. 212 is an armature for magnet 56. 213 is a link pivoted upon armature 212. 214 is a cam upon link 21.3, adapted to engage pin 205. 215 is a link connecting link 213-and armature 206. 216 is a flange upon shaft 200 in engagement with one of the springs of the pair 7 3, 'holdin said pair separated and extending in such irection and for such distance that such engagement of the flange with one member of the pair continues throughout the motion of thewipers in the first or primary direction ofsele'ction and that the engagement f is discontinued when the wipers make their first step :in the secondary direction, at which time by; the release of such engagement of the spring withthe flange the contact between the two springs of the pair is permitted, and the oil norihfalswitchg73 is closed. This switch detail is illustratedfurther in Fig. 4, which is takeiiiiit an angle of ninety-degrees with Fig. 3, the shaft 200 flange 216 being shown in section. v

The operation of the auton. iaticf switch and shown diagrammatically. i11-Fig. 31is -..as. fol v lows: By successive energizatiofis 'ot'magnet 54 armature 206 is attracted successively and driving'pawl 207 acts p sive. teeth-of the cylindrical rack, the rack being held-in its determined position by detent 'pawl"--203.

Then successive energizations of magnetf55 attract armature 209 successively, causing driving-pawl 210 to act upon successive teeth of cylindrical ratchet 202, turning it step by step in the direction indicated by the arrow, the cylindrical ratchet being held in its deter,-

mined position by the detent-pa'wl 203. Then energization of magnet 56 attractsarmatur'e 212, thus advancing link 213 until cam 2'14 passes pin 205, which it is permitted to do by 1 reason of the'slotted connection between link 213 and link 215. of magnet 56 armature212 is returned by spring tension to its position of rest, withdrawing link 213, causing cam 214'to engage pin 205, withdrawing detent-pawl 203, and releasing shaft 200 and wipers 80 81 82 to return to the normal position of rest by spring tension or gravity. Then upon the next energization of magnet 54 the movementof armature 206, acting through link 215,'lifts link 213 to disengage cam 214 from pin 205 and release detent-pawl 203 for service, as above described.

The operation of the trunk equipment, as a whole, is as follows: By the action of automatic switch 16,consequent upon the closing of the circuit at substation 10, the trunk, as 24 25 is selected and the signal 40 of that trunk is caused to be displayed by current from battery 27. There is no further change in the circuit conditions of elements 10, 16, or 40 until the termination of the conversation.

In response to the display of signal 40 operator at 41 presses key 46, which is adaptei. to remain in its depressed position until re leased by the hand of the operator. places the operator at 41 in telephonic communication with the patron at the telephone 10. She asks 'for and receives his order. the execution of the order she depresses key 47, which remains in its operated position until released by her hand, then depresses key Then upon deenergization This 51, which remains in its operated position until released manually by key 50 or electromagnetically by magnet 57,-then depresses key 49, which remains in its operated position until released manually by key 48 or electromagnetically by magnet 58, then controls and operates automatic selecting-switch 23 by the use of keys 52 53.

By the operation of key 51 battery 59 has been connected by conductors 60 61 62 with 'conductor '63, to which conductor battery 64 also is connected by conductors 65 66, the lat-...

ter containing the winding oimagnet 54; but magnet 54 is not energized'as the two batteries are equal in potential and opposing in polarity. 1 By the o eration of key '53 path is formed for current om grounded battery 64 over conductors 66 63 62 67 and to ground,

energizing magnet 54 successively for each 0 eration of the key 53, thus accomplishing t efirst selective movement of the automatic switch 23 and selecting the desired group of trunks or sets of waiting contacts. Having thus selectedthe group key 52 is depressed once by the operator, giving path for current from grounded battery 64 over conductors 65 68 69 70 71 72 and toground, energizing .magnet 55 and moving the'wipers one step in theirsecond. direction.

Switch 73 now becomes effective, its con struction being such that the two parts have a normal tendency toclose together, but one part being engaged with a projection of the wiper-carriage or moving-part of the automatic switch 23, the engagement beingmechanically such that the two parts of switch i 73 areheld out of connectionduring suchv time as the wiper-carriage is in its-normal positioni with reference to its secondmotion 0 selection regardless of its position with reference to the first motion of selection. Switches of this'nature are well known in the art both in function-and construction, and the name off-normal is applied tothem.

The energization of magnet 55 has ste first set of the waiting contacts of the selected group, and if wiper 80 findsa ground upon the waiting contact connected with circuit will be closed for current from battery 64' over conductors '68 74 75 79 80.83 84 and to ground, resulting in the reenergization of magnet 55 upon the, release of its vibrating armature, and thus the vibration'will continue until a waiting contact not grounded is engaged by wiper 80, at-which time, conductor 79 being open, current will flow from battery 64 over conductors 65 68 7 75 76 73 77 78 and to ground.

As mentioned, the relation of'relay 56 to magnet55 corresponds'to that of relay 19 to magnet 18, and therefore relay 56 is energized and magnet 55 is not energized. Con:

' sequent upon the energization of. relay 5O conductor 79'is removed from'conductor .75

p ped' the wipers forward into engagement w t the and connected with conductor 85, thus grounding conductor 84 and its multipled waiting contacts and placing busy test upon the selected trunk or line. Also by the energization of relay 56 conductor 63 is removed from conductor 66 and connected to wiper .82, and conductor 70 is removed from conductor 69 and connected to wiper 81. Conductors 69 66 are thus isolated, and further operation of magnets 54 55 is impossible so longas the energization of relay 56 continues by gc urrent through key-47. Conductors 63 70 now are connected through wipers 82 81 to conductors 87 86 and .thusto the modified Strowger switch,(indieated as a whole as 88;) The mechanical construction of this switch is well known in the art and is diagrammatically shown in Fi 5, wherein 300 is the shaft'bealring the insu ated wipers 100 101 102. 301 is 307 is the driving-pawl, pivoted upon the'ar 302 is the-cylindrical ratchet for,

mature 306. 308 is a fixed pin acting asa guide for the drivingawl 307. (armature of horizonta magnet 125. 310 is the driving-pawl, ivoted upon the armature 309. 3-11 is a xed pin actingas guide to the drivingawl 310/ 312 is the armature of. the relieasemagnet 108i adapted by its ook form to'engage pin 305 and withdraw pawl "303 when magnet 108 is energized. 121 is an off-normal switch closed by the first vertical movement of; the shaft 300. 317. is a side switch or auxiliary switch or pilo tswitch designed to be propelledbycontrol of private magnet. 94. is the armature of the'private magnet 94.

309 is the 31.3.is a link pivoted u on the armature 312 and loo 319 is a driving-pawl pivoted upon the arguide to driving-pawl 319. .Driving pawl mature 318. 320 is a fixed pin acting as a 319 is adapted to. pass one tooth of the part 317 when the armature 318 is attracted and to move thepart 317 by pulling the tooth thus passed when armature 318 re turns to itsposition of rest by s ring tension after being released magnetical y. y 96 97 are insulated wipers upon the side switch part 317. It is seen that by the first action of the prlvate magnet 94 the-wi ers'95 96 97 will 'be' advanced to their mi dle positions, whlle by the second action of the private magnet they will be advanced to their third or ast positions, after which no further advancement is possible. 316. is acollar' upon the shaft 300, adapted-to operate the ofi-normal switch 121 and also to restore the side switch part 317 to its normal position of rest upon the return of the shalt 300 to its normal position of rest .upon disconnection When released by the detent-pawl 303. Wipers 95 96 97 are so spacedupon the side switch that wiper- 97 lags behind the other two Wipers both in leaving the contact-points immediately after the starting ofthe'side switch under the pull of pawl 31 9 and in making connection with the next contact-point just before the side switch reaches the limit. of its step.

By another series of actuations key 53 controls switch 88 over the circuit from grounded batter 89 over conductors 90 91 87 82 63 62 67 an to ground, thus energizing the vertical magnet 92 successively and selecting the desired level of waiting contacts. by theoperation of key 52 current is taken from battery 89-over conductors 90 93 86 81 71 72 and to ground, energizing and releasing the private magnet 94 and stepping the side switch-wipers 95 96 97 forward one ste in the well-known manner.

y another series of operations of the key 53 switch 88 is controlled by a circuit from grounded battery 89 over conductors 98 87 82 6362 67 and to ground, stepping the wipers 100 101 102 forward into contact with the selected, telephone-lineby energization of rotary magnet 125.

If the line thus selected be busy, it will have the condition of busy testnarnely, a ground upon the terminal connected with by private wiper 102. The presence of the busytest ground will give path for current from battery 89 over conductors 90 99 103 104 97 105 102 106 107 and to ground, energizing release-magnet 108and resto'ring the wipercarriage to its normal position of rest. Thus restoration will occur without the magnetic release of key 51, which is provided for in the next paragraph.

If the line selected be not busy, then the actuation of key 52 subsequent to the last selective group of actuations of key 53 will energize and release private magnet 94, and thus step the si e-switch wipers 95 96 97 for- Ward into their right-hand position. In the motion of the si e-switch wipers from the middle to the right-hand position the sequence of the breakings andmakings of connections is as follows: First, wipers 95 96 break from conductors 98 93, respectively; second, wiper 97 breaks from conductor 104; third, wipers 95 96 make contact with conductors leading to wipers 101 100, respecvtively, and thus circuit is completed for current from grounded battery 59 over conductors 6O 61 62 63 82 87 95 101 43 29 and to ground, energizing magnet 57 and releasing key 51. The release of the key 51 immediately succeeding the last actuation of the key 52 indicates to the operator that the line se- Then lected has been connected with. Fourth,wi er ground, energizing relay 19, but not energizing relay 18. The energization of relay 19 removes the ground from conductor 29 and connects conductors 29 38.'to wipers 22 21, these wipers being out of connection with any waiting contacts. The connection of conductor 33 also is changed from conductor By the automatic release of key 51 path is given for ringing our- 32 to conductor 37.

rent from ringing-generator 115 over conductors 113 11,1 70 81 86 96 100 44 116 1543 101 95 87 82 63.110 112 and to ground. From junction-point 116 a branch circuit exists over conductor 28 and through battery 27 to ground The current flowing over this .branch path is not designed to actuate the armature of relay 17, since relay 17 is of considerable impedance and is designed to be energized by continuous current; but such actuation would not in any way affect the operation of the circuits shown, since the armature would but place ground upon conluctors 35 and-34, both of which are already grounded, the. former through 42 106 1.02

.105 97 109and the latter through 20 33 37. Owing to the high resistance of element 13 in the main ringing-circuit traced above magnet 58 does not receive suflicent current to energize it to the degree re uired to attract its armature. The signal-be l 13 is actuated by the current flowing through it. sponse to this signal the patron at substation 10. lifts the receiver from the hook, and thus substitutes the low resistance of conductor 11 for the high resistance of elements 12 and 13, formerly connecting conductors 15 and 14. This reduction of the resistance of the main ringing-circuittraced above results in an increase of the volume of current flow- In reing through that circuit, anl therefore results in a greater energization of magnet 58. Magnet 58 attracts its armature, and therefore releases key 49, indicating to the tele phone operator that the called station hasanswered, and also connecting the called line through to the calling-line by connection be tween conductors 110 111 and conductors 117 1.18. Path is furnishel also for current from grounded battery 27 over conductor 28 15 11 14 4310195 87 82 63110117119 and to ground, energizing relay 17 without consequent effect and energizing visual signal 45. Current will continue to flow through this path without change throughout the duration of the conversation, furnish energy for speech transmission from station 10 and.

cause signal 45 to remain displayed before the o erator. s If rev 51 had not released automatically immediately upon the last actuation of se-.

lective key 52, the 0 erator would under-' stand that the line se ected had been found busy andwould so report by telephone to the calling patron. If within a reasonable time the ringing-key 49 had not been released automatically and signal 45 had not been displayed, the operator would understand that the called party had not answered and Would 4 2 5 noted that in the selection of the trunk 83 -86.

87 by the switch 23 and the consequent energization of relay 56 the grounded conductor 85 was connected to trunk conductor 83 and furnished path for current from battery 89 s over conductors 90 99 83 8O 79 85 and to ground, energizing relay 120, the winding of,

which forms a portion of conductor 83. This relay during its energization breaks connection between conductors 122 and 123.

Electric .switch 121 is an off-normal switch similar in all respects to the off-normal switch 73 of automatic switch 23, and likewise is closed by the first rotary step of the modified Strowger switch 88.

- The release-magnet 108 differs from the switching and release magnet 56 in its me- Y chanical relation to the switch 8 8. The release-magnet 108 is adapted to restore switch 88 upon energization and not consequent upon deenergization.

Wenow will pass to the consideration of the disruption of the connection set up and the consequent restoration to normal of all parts used.

By hanging the receiver upon the hook at substation 10 direct current previously flowing through conductors 11 and 1-19 is interrupted and signal 45 ,isreleased. By'hang ing receiver upon the hook at substation 10 current flowing through conductors 11 and 39 is interrupted and signal 40 is released.

The breaking of circuit for direct current through substation 10 has deenergized relay 17 and by release of the armature-of that re- 6c lay has interruptedcurrent through relay 19,

by the deenergization of which the mechanisms associated with its armature have effected the restoration of switch 16 as a whole to its position of rest. .Upon the release of I the signals 40 and 45 the operator will manually release the key 47, disconnecting conductor 77 from conductor 78 and interrupting the current previously flowing'to ground at 78 from battery 64 over conductors 65 68 74 75 76 73 77 78 and which has maintained the energization of relay 56. By the interruption of that circuit and the release of the armatures of relay 56 the mechanisms assoc1- ated with those armatures have eflected the restoration to normal of the switch 23 as a whole. I

By the restoration of the switch 23 ground conductor has been disconnected from conductor 83 and the circuit through relay. 120 is interrupted, thus releasing its arma-'- ture and closing'its circuit for current from battery 89 over conductors 90 99 103 121 122 1-23 and to ground, energizing release-magnet 108'and restoring connector. 88 as a Whole to its normal position of rest, including in such restoration the interruption of said restoringcircuit by the opening of the switch 121.

The restoration of the switch 88 to normal ,hasdisconnected ground conductor 109 from conductor 106,'and the breaking of the circuit through conductor 1 1 had previously interru ted the circuit through conductor 28" and eenergized relay 17, releasing its armature. Thus all grounds are removed from conductor 42- and circuit is interrupted for- Relay 19, therefore, is deenergized and switch 16 as a whole is restored to its normal position of rest. 1 The hanging .up of the two receivers at the who by release of er key 47 in conjunction with the hanging up of the receivers has restored all parts to a normal position of rest in readiness for a succeeding call involving any or all of them.

'merly giving current through conductor 36.

IOO

substation-telephones in connection thus 'aujtomatically has si naled the operator at 41,

I do not wish to limit myselfin all respects in the inter retation of my invention to the particular evices or circuits herein shown, as many variations may be made without departing from the spirit or scope of my invention. For instance, no indication is given,

either in the drawings or in this written de scription, indicating the relative locations of the equipments 16, 23, 88, and 16. Thus the figures shownare applicable to an instal- IIO lation in which all of these parts are placed 7 inthe same central office or to one in which the different parts are distributed in any desiredmanner among a plurality of central oflices, the length of the connecting trunk Conductors, as 24 25, 63 7O 77, 83 86 87, 42 43 44, not being a limiting factor in the op- I eration of the system as applied to exchange areas of present commercial size.

.In the description herein given an we "change district is considered involving directory numbers of three digits and in which one digit is cared for by switch 23 and the reswitches 23 would be required, and these might be all in one central office or distributed through many central offices.

A single automatic calling device may be substituted for keys 53 and 52. As key 51 connects those selecting-keys to the trunk under actuation and disconnects them upon release, but one such automatic device would be necessary for each operator. This modihcation is shown in Fig. 6, the mechanism of the well-known Strowger device being indicated n connection electrically with the key 51 and associated circuits of Fig' 1, the necessary circuits of theStrowger calling device itself being shown iii-dotted linest .Any form of inductive link may be substituted for the condensers 124-.

In the. drawings I have shown grounded batteries 27 59 64 8 9 27, all of which are of the'same potential and polarity. As many of these batteries as are placed in the same central office may be combined, or, in other words, one battery may be used in each centraloiiice and all conductors taken to it.

Many other variations are possible without departin from the spirit of my invention.

WhatI claim,therefore, and what I desire to secure by United States Letters Patent, 1s-

1. In a telephone system, the combination of a substation-telephone, a central office, a trunk-selecting switch in said central office,

I a line connecting said substation-telephone with said trunk-connecting switch, speechtransmltting elements forming a art of said substation-telephone and adapte" to receive electrical energy for speech transmission from said connecting telephone-line, a source of electrical potential in said central office, a relay in said central office and connected to said line, a trunk in said central oflice, a visual signal, and a circuit including said source of potential, said relay, said line, said speechtransmitting elements, a conductor in said trunk and said visual signal, substantially as described.

2. In a telephone system, the combination of a substation-telephone, a central office, an automatic switch in said central office, a

grounded source of electric energy in said central office, a relay in said central oi'lice, a telephone-line extending between said substaticn-telephone and said central office; a switch controlling circuit extending from ground through said source of energy, said re lay, a limb of said line, the speech-transmitting elements of said substation-telephone,

the remaining limb of said line and to ground a trunk; a visual signal; and a supervisory circuit extending from ground through said source of energy, saidrelay, the limbs or said line, the speech transmitting elements of said substation-telephone, 'a C(TIlilllCtGl of said trunk, said visual signal and to ground;

said first-mentioned circuit and said second-' mentioned circuit being effective alternatively, substantially as described. 7

3. In a telephone system, the combination of a substation-telephone, a central office, a line connecting said substation-telephone with said central office and comprising two limbs, a relay having an inductive winding in said central oi'fice, a source of electrical potential in said central office, speech-transmitting elements at said substationconnected between the limbs of said line, a trunk, a signal devicefassociated with said trunk and having an inductive winding balancing inductively the inductive winding of said relay, means forconnecting said line and said trunk, anda circuit including said source of potential, said relay, the two limbs of said line, said speech-transmitting elements and said signal device, siibstantially as described.

4. In a telephone system, thecombination of an automatic switch adapted to connect a telephone-line to a selected trunk, a tele "phone-substation, a telephone-line connect ing said substation-telephone with said automatic switch, a relay associated with said automatic switch, a source of electrical potential, a circuit extending from ground through said source of electrical potential and the windings of said relay to one of the limbs of said line, a selected trunk, a signal device associated with said trunk, a circuit extending from ground through the'winding of said signal device and a] conductor of said trunk, and through the selecting contacts of said automatic switch to the other limb of said telephone-line and speech-transn'litting elements forming a part of said substation-telephone and connected between the two limbs of said line, substantially as described.

' 5. In a telephone system, the combination of a substation-telephone, a central office,'a relay having an inductive winding in said central oiiice and associated with said line, a

source of electrical potential in said central office, a plurality of trunks in said central office, means for com'iecting, said telephoneline with a selected one of said trunks, avisual signal having an inductn e winding and associated with said selected trunk, and a circuit comprising said. source of potential, said iu ductive winding of said relay, said telephoneline, the speech-trans1nitting elements of said telephone, a conductor of said trunk, and said inductive winding of said signal device, substantially as described.

6. In a telephone system, the combination of a substation 10, a line 14. 15 connecting said substation to a central office, an automatic switch 1.6 in said central oflice, a trunk 24 25 leading fronrsaid automatic switch to an operator, an .operators equipment 41 adapted to be associated with said trunk, an automatic switch 88 adapted to be associated with saidjtrunk, keys forming a part of said operators equipment and adapted to con trolsaid automatic switch 88 when it is associated with said trunk, and a plurality of lines as 14' 1 5 selectively accessible to said automatic switch'88, substantially as described.

7. Ina telephonesystem, the combination a of a substation 10, a line 14: 15 connecting said substation with a central ofiice, a trunk in sald central oflice, an automatic switch 16 adapted to connect said line with said trunk,

an operators equipment, keys forming a part a of said operators equipment and associated with said trunk, an automatic switch 23 associated with said trunk andad'aptcd to be controlled by said keys, an automatic switch'88' .adapted to be associated with said trunk and adapted to be controlledby said keys when so associated, and. a plurality of lines as 14- 15 selectively accessible to said automatic switch 88, substantially as described.

8. In atelephone-system, the'combination.

of a substation-telephone 10, a line 14' 15 connecting said substation-telephone to an automatic switch 16, an automatic switch 16 adapted to connect said'tele'phone-line to a trunk, a trunk, a first. circuit including a source of electric potentiahthe speechtrans mitting elements of said substationtelephone, said line, said automatic switch 16, and a portion of said trunk; an automatic switch 88 controlled manually by a'centraloffice operator, ayselected telephone-line 14. 15, a substation-"telephone 10 on said selected telephone-line, 'asecond circuit including a source of electric potential, the speechtransmitting elements of said substation-telephone 10, said selected telephone-line, said' automatic switch 88, and the remaining portionof said trunk; and an inductive link connecting together said first circuit and said second circuit for speech transmission between the two said substation-telephones,

substantially'as described.

9. In a telephone system, the combination of a substation-telephone, a central oflice, a

line connecting said substation with said cen tral 'ofiice, speech-transmitting elementsforming a part of said substation-telephone adapted to transmit speech by energy received over said telephone-line, an automatic switch in said central oliicc. connected to said line and adapted to connect said line with a trunk leading to an operators equipment, the trunk, an automatic switch connected with said trunk and adapted to said operators control and. adapted to connect said trunk to a selected line, a substation on said selected line, speech-transmitting elements in said latter substation adapted to transmit speech by energy received over said selected line, a circuit including a central-hfiice source of electrical potential and said speech-transmitting elements of saidfirst substation, an

independent circuit including a source of electrical potential in said central office and the speech-transmitting elements of said latter substation-telephone, and an inductive link connectings aid circuits adapted to transmit alternating currents between said circuits, substantiallyas described.

10. In a telephonesystem, the combination of a substation. telephone, a central o l'lice, a line connecting said telephone and said central oflice, trunk-lines .wholly within said central oliice and adapted at one end to be. selected by a telephone-line and at the other end to select a telephonedihe, an automatic switch connected-to said telephoneline for. selecting an idle one of said trunks,

keys connected with said selected trunk for controlling its selecting end, and visual signals connected to said selected trunk and adapted to be controlled by substationtele" phones connected to said trunk, substan tially as described.

11.. In a telephone system, the combinatele hone withsaid trunk, means associated wit said trunk for connecting with a selected one of aplurality of telephone-lines, a key .associated'with said trunk having electromagnetic release and adapted to be released consequent upon connection with a selected I telephone-line, another key-associated with said trunk'adapted to connect a source of ringing energy to said selected line and having electromagnetic release adapted to release said key upon the answering of a-substation-telephone upon said selected telephone'-line,1.and' a visual signal associated with said trunk adapted to be displayed while the receiver is off the hook at a substation-telephone upon said selected telephone-- line, consequent to the release of said keys, substantially as described.

12. In a telephone system, the combina- 1 tion'of a substation-telephone, a central office, a line connecting said telephone and said central oflice, trunks within said central office, an automatic switch associated with said line, and adapted to connect selectively with an idle one of said trunks, a visual signal associated with said selected trunk, and

adapted to be displayed when said trunk is connected with, an operators telephone equipment, a key for connecting said operators telephone with said trunk, means associated with said trunk for connecting with a selected one of a plurality of telephonelines, a key associated with said trunk having electromagnetic release and adapted to be released consequent upon connection with a selected telephone-line, and a visual signal associated with said trunk adapted to be-displayed while the receiver is off the hook, at a substation-telephone upon said selected telephone-line, substantially as described. 13. In a telephone system, the combination of a substation-telephone, a central o'ffice, a line connecting said telephone and said central office, trunks in'said central office, an automatic switch associated with said line and adapted to connect said line selectively with an idle one of said trunks, a relay controlling said automatic switch, a source of electric potential in said central office, speech-trans1nitting elements in said substation adapted to transmit speech by energy received over said line, a visual signal associated with said selected trunk, a circuit including said source of potential, said relay, said line, said speech-transmitting elements, and said signal, an operators telephone, keys for connecting said operators telephone with said trunk, an automatic switch asso ciated with said trunk for selecting a telephone-line, a selected telephone-line, a substation-telephone upon said selected line, speech-transmitting elements in said latter substation-telephone adapted .to transmit speech by ener y received over said line, keys associated wit said trunk for controlling said latter automatic switch, a key associated with said trunk for impressing ringing energy upon said selected telephone-line, a key associated with said trunk, for maintaining connection between said trunk and a-selected telephone-line and for disrupting s'aid connection, another visual signal associated with said trunk, a second circuit including said source of potential, said selected line, the speech-transmitting elements of said latter substation-telephone and said other visual signal, and an inductive link connecting said first circuit with said second circuit, substantially as described.

14. In a telephone system, the combination of a substation-telephone, a central ,office, a line connecting said telephonewith said central office, a relay in said centralv office, a visual signal in said central office, au-

circuit including a central office source of electrical potential, said relay, said line, said telephone,circuit-conductors passing through said automatic switch, and saidvisual signal, substantially as described.

15. In a telephone system, the combination of a substation-telephone, a central office, a line connecting said telephone with said central office, speech-transmitting elements in said substation-telephone adapted to transmit speech by energy received over said line, a relay in said central office, a visual signal in said central office, automatic switch in said central office, and a circuit including a central-office source of electrical potential, said relay, said line, said speech-transmitting elements of said telephone, circuitconductors passing .throughsaid automatic switch, and said visual signal, substantially'as described.

Signed by me at Grand Rapids, county of Kent, and State of'Michigan', in the presence of two witnesses.

EDMUND LAND.

Witnesses PETER DORAN, H. H Inn.

.tomatic switch in said central office, and a 

